This invention relates to safety devices for electric appliances and, more particularly, to a safety device which prevents an electric appliance or the like from inadvertently starting when the appliance is plugged into an electric outlet with its switch in the on state.
If an electric appliance or tool which has an on/off switch is plugged into a live AC outlet when the switch is in its on state there is the possibility of both personal injury and property damage occurring. Similiarly, if power is lost while such appliance or tool is being utilized and the operator neglects to turn the device off prior to power restoration, when power is restored the same type of injury or damage may occur. Exemplary devices with which this problem exists include an electric knife, electric food mixer, electric blender, electric food processor, electric drill, electric router, electric hand saw, electric sabre saw, electric buffer, electric sander, electric hedge trimmer, and electric lawn mower. Many other potentially dangerous devices exist which are subject to the same type of inadvertent operation. It would therefore be desirable to be able to prevent such inadvertent operation of an electric appliance, tool, or the like.
It is therefore an object of the present invention to provide a safety device for use with an appliance having an on/off switch which prevents the appliance from operating if power is applied to the appliance when the switch is in the on position.
Various devices have been proposed to prevent such inadvertent operation of an appliance. An example of such a device is disclosed, for example, in U.S. Pat. No. 2,985,800. However, such devices generally suffer from a number of disadvantages. For example, many of these devices are built into the appliance and are physically interconnected with the power-supplying switch of the appliance. These devices generally include a relay and require that the power-supplying switch of the appliance be a single pole double throw switch arranged to supply power to the relay coil only when the switch is in its off position. The relay is then locked on by a normally open contact thereof, which contact then allows power to be applied to the appliance when the switch is subsequently moved to its on position. Problems with such a device include the fact that it is dedicated to the appliance and also that it requires a special switch.
It is therefore another object of this invention to provide such a device which does not have to be built into the appliance so that it can be utilized to protect appliances which are already in the hands of consumers.
It is a further object of this invention to provide such a device which is operative with an appliance having a single pole single throw power-supplying switch.
It is yet another object of the present invention to provide such a device which is functional with variable speed appliances.
It is still a further object of the present invention to provide such a device which may be plugged into an AC outlet and into which may be plugged an appliance, or which may be built as part of the line cord assembly of the appliance, or which may be built into the appliance itself, or which may even be installed in an outlet box.